The invention pertains to a process and a device for determining the internal condition of wooden structures such as trees located along roads, on plantations, in parks, or in forests, for the purpose of evaluating their state of health, as well as wooden poles or wooden components in bridges, buildings, or frame structures for potential damage caused by plant or animal pests.
In addition to the non-destructive methods utilized for determining the internal condition of trees or wooden components through the use of ultrasound, X-rays, or the like, procedures are generally known to exist in which the test object is drilled open and information is obtained about the wood's internal condition by examining the bore hole, e.g. through the use of an electric probe, or by examining the wooden material removed by drilling. Such procedures, however, are either too expensive because of equipment costs or else they result in a substantial reduction of the test object's strength characteristics.
A device and a process have already been proposed for eliminating these disadvantages, whereby a spring-loaded needle is inserted into the wood and the penetration resistance is measured on the basis of the depth of penetration (Forstw. Cbl., Vol. 81, 1962, 7/8, 222-230). The results obtained from this procedure are quite imprecise, however, and permit one to make only a rough estimate about the internal condition of the test object. This is especially true as the depths of penetration become greater, since the results are falsified to the extent that the frictional contact surfaces of the needle with the wood grow larger. In spite of this, such a needle-based procedure is preferred by specialists because it causes no appreciable damage to the strength characteristics of the wood being evaluated.
The purpose of the invention is therefore to improve upon the needle-based procedure in such a way that it will produce results which are considerably more precise, while at the same time retaining its practical utility for taking measurements at reasonable cost.
As specified by the invention, this purpose is fulfilled by means of a process in which the needle is rotated, whereby the diameter of the needle's head is greater than the diameter of the needle's shaft, and where power consumption by the needle's rotary drive mechanism and/or feed drive mechanism is measured during penetration.
The process upon which the invention is based provides results which are reliable and error-free because, during insertion of the rotating needle with its somewhat enlarged head, only those forces which are analogous to the internal condition of the wood are able to act upon the head of the needle, so that the measurement of power consumption on the part of the needle's drive mechanisms provides a precise profile of the wood's inner structure, dependent to an accurate extent upon the respective position of the needle's head, i.e. the depth of the needle's penetration.
The operator is able to observe the measurement results optically, as well as acoustically based on changes in the sound of the needle's motion, so that such an operator already obtains in advance a rough indication of the wood's condition. In accordance with a practical working variant of the invention, such results can also be made visible for detailed evaluation on a screen, recorded on a moving graph, and/or stored on an electronic data carrier.
In one preferred working variant of the process upon which the invention is based, the power consumption of the needle's drive mechanisms is determined by measuring the input of electrical current by the needle's rotary drive and/or its feed drive during penetration. Consumption during idling, and thus the natural power losses of the drive mechanisms, have no influence upon the measured result.
Alternatively, power consumption by the drives can also be determined by measuring the change in the rotary speed of the rotary drive and/or the change in the forward speed of the feed drive during the needle penetration process.
It is also possible to determine power consumption by measuring the change in torque for the rotary drive and/or the change in forward thrust for the feed drive during penetration.
All of these variations of the process upon which the invention is based can be carried out with or without a constant forward speed for the needle's feed drive.
One practical device used for carrying out the procedure makes provision for a needle consisting of a steel wire with a length no greater than the maximum thickness of the test object and with a generally constant shaft diameter of less than 2 mm, whereby the head of the needle forms a flat, triangular tip possessing a rotational diameter greater than 2 mm. Excellent measurement results were obtained in initial tests using a needle having this shape, and using the process upon which the invention is based. In terms of precision, such results far surpass all of the procedures and devices previously known to exist.
If needles with a very large axial length are required, one advantageous working variant of the invention makes provision for the needle to be passed through at least one support element which is movable relative to the needle during the penetration process, such passage taking place between the fixed end of the needle and its head.
It may be practical to cut a fine thread into the surface of the needle shaft, which thread transports the chipped or pulverized wood material out of the entry channel, thus keeping the needle shaft free from frictional forces which might impair measurement results in extreme cases where the wood is very moist or in a similar condition.